84

It's due to the larger relative apparent size of the Sun. When the source of light is a point source the shadow is harder, and when it is extended it is softer. Jupiter is approximately 5 times more distant from the Sun than the Earth, so the Sun is approximately 5 times smaller in the sky. *Source: University of North Carolina CS


40

What you are calling a focal point is the end of the umbra, the point at which the umbra changes to the antumbra. In a total solar eclipse, that point is below rather than above the surface of the Earth. An annular eclipse occurs when that point is above the surface of the Earth. The Moon appears to be smaller than the Sun, leaving an unbroken ring of the ...


39

In our solar system, it is possible for one planet to partially eclipse the sun, but it is not possible for any planet to cause a full solar eclipse as seen from another planet. The sun is too big and the planets are too small and too far apart. Transits occur, and can occur for any pair of planets, but they are very rare. As seen from earth, Mercury only ...


34

Glancing at a partial solar eclipse is about as dangerous as glancing at the Sun on any other day. If you look at the Sun a few minutes after sunrise or a few minutes before sunset, when the Sun's altitude is low, the light is filtered through a lot of air, and most of the ultraviolet is scattered, so it's a lot less dangerous than looking at the Sun in the ...


30

I did see the Venus transit before the Sun in 2004. I used no telescope, but of course I used proper solar eclipse glasses to protect my eyes. The black circle was small but clearly visible. But Mercury is much smaller, the transit is not visible without a telescope. See Wikipedia. Here an image of a Venus transit: Here the much smaller Mercury: The ...


29

Due to the basic proportionality theorem, the width of the boundary of the shadow is $$ w=\frac{\ell D}L\;, $$ where $\ell$ is the distance from the moon to the planet’s surface, $L$ is the distance from the planet to the sun, and $D$ is the diameter of the sun. Here \begin{eqnarray} D&\approx&1.4\cdot10^9\mathrm m\;,\\ L_♁&\approx&1....


27

I'll use the atmosphere as my big natural lens. So I'll watch the upcoming mercury transit at the sunset time where the sun looks bigger than usual. While the Sun and Moon might seem larger at the horizon, their angular size doesn't get larger. It's an optical illusion. Will this make the black dot of mercury bigger or big enough to be obviously seen by ...


26

During a sunset, the Sun is lower in the sky than during most of the day - much lower. Therefore, light from the Sun travels through about 120 miles of dense atmosphere, compared to the roughly 2 miles it travels through from straight up. Here's a rough sketch (not to scale) to demonstrate this. It is clear that $B>A$: Light scatters in the atmosphere; ...


23

Yes, observations of this kind are within the technical scope of amateur astronomers. Several groups succeeded in replicating the experiment during the 2017 eclipse that crossed the USA. For example Donald Bruns measured deflections of 2.8 arcseconds of multiple stars. Nasa published a "How To" page for anyone wanting to test GR themselves.


23

But how big is this shadow? How many kilometers is its diameter? That's a photo of the umbra and penumbra on the surface of the Earth taken from Space. It's a little distorted because it's not directly under the ISS but far off near the terminator. It's hard to pin down the size of the penumbra because it's fuzzy and fades near the edges, but if you could ...


22

The short answer is no. The alignment occurs, but the eclipse does not, due to the distances and size differences involved. There are a few things to consider here. You already mentioned a lot of them, I'll address those considerations separately. Alignment are alignements of the Sun and two planets actually possible (and if so, how frequent)? We can ...


19

The umbra has a well defined diameter but the size varies due to the eccentricity of the orbits of the Earth and of the Moon. The Moon may be so far away that it can't fill the solar disk at all (for instance Moon at apogee and Earth at perihelion). We can, however, theoretically determine the diameter of the shadow that the Moon casts on the Earth. The ...


18

The people who say it is an internal reflection are right. This is an internal reflection inside the lens of the camera. There is no actual object there. In particular, Venus is not visible this close to the sun even during a partial solar eclipse. Moreover, Venus is currently a very very thin sliver, no more than a scrape of light at the edge of the planet,...


18

It's an internal reflection. The dead giveaway is that in the second picture, the reflected image is a point reflection at the center of the image optical axis (assuming the image was not cropped). Using this information, I can predict that the crescent in the actual Sun (which is overexposed), would have the Moon take a bite out of the Sun at the 4 o'clock ...


16

The Moon orbits in a plane that is inclined with respect to the plane in which the Earth orbits. The intersection between these two planes is a straight line. For an eclipse to occur, this straight line needs to be roughly aligned with the line that goes between the Earth and the Sun. From this blog post As the Earth goes around the Sun, the plane in ...


15

As the Moon's eccentric orbit around the Earth brings it nearer and farther, current solar eclipses can be total or annular. A few in between are hybrid eclipses: total along the midday part of the path, and annular near the sunrise or sunset end. This happens mostly due to the Earth's surface curvature and partly due to the Moon's orbital eccentricity. ...


13

This webpage gives a lot of background information. Key points: It does seem to be the overall dimness of near-total eclipses that allows the pupil to widen enough to allow damaging levels of UV in. There are cases of eye damage from staring at the full sun, and also cases of staring at the noonday sun without apparent damage (not recommended). Perhaps ...


12

Another factor is involved in addition to the above answers. Io's umbral shadow is a bit over two million kilometers long, almost six times longer than the ~350 thousand kilometer distance between Jupiter's surface and Io. This means that most of Io's shadow on Jupiter's surface as seen from space is Io's umbral rather than its penumbral shadow. Io's umbral ...


12

I used the same lens flare effect (internal reflections from the camera's optical surfaces) to image the eclipse from my phone. The shape (as well as the location) was a symmetric reflection about the center of the lens. The color was probably induced by the spectral response of the antireflection coating in the lenses, which are not perfect or flat.


11

One thing to double check is if you can see stars easily at night from the same location. If there are city lights nearby, combined with humidity or dust you can have a bright sky due to terrestrial effects. Another thing to consider is the time needed for dark adaptation. If you walk from a brightly lit room out under a dark sky, you can't see many stars ...


11

Consider how far the pleiades are above the ecliptic, and how far the moon travels in a day. From this you can work the angle at which the moon must travel relative to the ecliptic, in order to cross the eliptic within a day. You can then compare this with the actual inclination of the moon's orbit to the ecliptic, and that will tell you if an eclipse is ...


10

Calculation of solar eclipses can be done using Besselian elements. The basic idea is to compute the motion of the Moon's shadow on a plane that crosses the Earth's center. Then, the shadow cone of the Moon can be projected on the Earth surface. The Besselian elements are the following: X and Y: the coordinates of the center of the shadow in the ...


9

Solar and lunar eclipses occur about equally often - between two and four times per year. However, when you do not intentionally travel around the world chasing solar eclipses, you are more likely to observe more lunar eclipses. The reason is that solar eclipses can only be observed from a comparatively small area while lunar eclipses can be observed from ...


9

I will take a stab at it. Assuming the last eclipse happens when the moon is at perigee and the earth is at aphelion. the moon's perigee is increasing by 4 cm per year, the earth's aphelion does not change with time, the sun and the moon are perfect spheres, the radius of the sun and moon don't change, and a total eclipse occurs when $r_{\mathrm{sun}}/d_{\...


9

Yes, but such an event would be very rare. Venusian transits last only about 7 hours, and there are only two in 113 years, So Venus is in transit for about 0.0015% of the time. So as a back-of-the-envelope calculation, you would need to see about 70000 eclipses before you had a combined transit/eclipse. There are about 2 solar eclipses a year, so you might ...


9

The Moon's orbit about the Earth is only approximately elliptical. The Moon's orbit precesses both axially and nodally, and the eccentricity of the Moon's orbit varies. That the Moon's orbit precesses axially means that perigee sometimes occurs when the Moon is close to new, sometimes when it is close to half-full, and sometimes when it is close to full. ...


9

Draw a picture of Sun, moon, observer, as viewed from the side: SSSSSSSSSSSS \ / \ / \ / \ / MMMM \/ Since the triangles formed by the diameter of the sun and the observer, and the diameter of the moon and the observer are similar, you can write down the connection between the given distances using length ratios, or ...


8

If it's not safe to look at the sun's reflection in the water normally then it's no safer during an eclipse because even if 1% of the sun is showing this is more than enough light to seriously damage your eyes. The best way to view the sun, if you haven't ordered your eclipse glasses yet, is to poke a hole in a piece of paper and project an image of the sun ...


8

It seems that the station has, in fact, given out extremely dangerous advice - simply because it was poorly phrased. Viewing a solar eclipse is incredibly dangerous - mostly under circumstances where you're looking towards the Sun. As Wikipedia warns, Looking directly at the photosphere of the Sun (the bright disk of the Sun itself), even for just a few ...


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